At a security conference in Singapore, US Secretary of State Mike Pompeo accused North Korea and countries including Russia of continuing to violate UN sanctions aimed at pressing the North to give up its nuclear arsenal.

But at the same time, he oversaw the handover of a letter to North Korean leader Kim Jong Un from US President Donald Trump and exchanged pleasantries with the North’s foreign minister Ri Yong Ho.

Mr Ri, meanwhile, greeted Mr Pompeo with a smile and posed for photos – but then delivered a scathing attack on the Trump administration for approaching the negotiation poorly by insisting on sanctions enforcement.

Mr Ri said North Korea would not be forced into acting unilaterally, and demanded that the US undertakes “confidence-building” measures if the negotiation is to be successful.

After Mr Pompeo warned once again that no sanctions would be lifted until North Korea fully and finally denuclearises, Mr Ri told the annual ASEAN Regional Forum that the North will not be bullied into concessions.

“Confidence is not a sentiment to be cultivated overnight,” he said. “In order to build full confidence between the DPRK and the US, it is essential for both sides to take simultaneous actions and phased steps to do what is possible one after another.

“Only when the US ensures that we feel comfortable with and come close to it, will we be able to open our minds to the US and show it in action.”

The US has previously dismissed calls for a phased approach, insisting that sanctions be maintained until the North delivers on its commitments but suggesting some other steps may be possible.

Mr Ri, though, appeared unmoved and accused elements of the US government of going against Mr Trump’s wishes by taking a hard line on sanctions.

“What is alarming, however, is the insistent moves manifested within the US to go back to the old, far from its leader’s intention,” he said.

Instead of responding reciprocally to North Korea’s suspension of nuclear tests and missile launches and other goodwill gestures such as the return of suspected remains of American troops killed in the Korean War, the US has maintained hostility, Mr Ri said.

“The United States, instead of responding to these measures, is raising its voice louder for maintaining the sanctions against the DPRK and showing the attitude to retreat even from declaring the end of the war, a very basic and primary step for providing peace on the Korean Peninsula,” he said.

He also accused Washington of taking “extremely inappropriate moves” by discouraging third countries from sending high-level delegations to the North’s 70th-anniversary celebrations in September.

Mr Pompeo had already left the meeting in Singapore when Mr Ri delivered his remarks in order to travel to Jakarta for talks with senior Indonesian officials. As he arrived in Jakarta, the State Department said that a written reply to Mr Kim from Mr Trump had been delivered to Mr Ri in Singapore.

Earlier on Saturday, Mr Pompeo warned Russia, China and other countries against any violation of international sanctions on North Korea that could reduce pressure on the North to abandon its nuclear weapons.

His comments came on the heels of a new United Nations report that found North Korea has not stopped its nuclear and missile programmes and is violating UN sanctions, including through illicit ship-to-ship transfers of oil.